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INTERNET DRAFT                                Mallikarjun Chadalapaka
draft-ietf-ips-iscsi-impl-guide-01.txt            Hewlett-Packard Co.
                                                               Editor


 
 
 
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                        iSCSI Implementer's Guide 

                                        

Status of this Memo 
     By submitting this Internet-Draft, each author represents 
     that any applicable patent or other IPR claims of which he or 
     she is aware have been or will be disclosed, and any of which 
     he or she becomes aware will be disclosed, in accordance with 
     Section 6 of BCP 79. 

     Internet-Drafts are working documents of the Internet 
     Engineering Task Force (IETF), its areas, and its working 
     groups.  Note that other groups may also distribute working 
     documents as Internet-Drafts. 

     Internet-Drafts are draft documents valid for a maximum of 
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     than a "work in progress." 

     The list of current Internet-Drafts can be accessed at 
     http://www.ietf.org/1id-abstracts.html 

     The list of Internet-Draft Shadow Directories can be accessed 
     at http://www.ietf.org/shadow.html.  

Abstract 
     iSCSI is a SCSI transport protocol and maps the SCSI family 
     of application protocols onto TCP/IP.  RFC 3720 defines the 
     iSCSI protocol.  This document compiles the clarifications to 
     the original protocol definition in RFC 3720 to serve as a 
     companion document for the iSCSI implementers. This document 
     updates RFC 3720 and the text in this document supersedes the 
     text in RFC 3720 when the two differ. 




 
 
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     Table of Contents 

     1       Definitions and acronyms ...............................3 
     1.1     Definitions ............................................3 
     1.2     Acronyms ...............................................3 
     2       Introduction ...........................................5 
     3       iSCSI semantics for SCSI tasks .........................6 
     3.1     Residual handling ......................................6 
     3.1.1  Overview..............................................6 
     3.1.2  SCSI REPORT LUNS and Residual Overflow................7 
     3.2     R2T Ordering ...........................................8 
     4       Task Management ........................................9 
     4.1     Requests Affecting Multiple Tasks ......................9 
     4.1.1  Scope of affected tasks...............................9 
     4.1.2  Updated semantics.....................................9 
     4.1.3  Rationale behind the new semantics...................11 
     5       Discovery semantics ...................................13 
     5.1     Error Recovery for Discovery Sessions .................13 
     5.2     Reinstatement Semantics of Discovery Sessions .........13 
     5.2.1  Unnamed Discovery Sessions...........................14 
     5.2.2  Named Discovery Sessions.............................14 
     5.3     TPGT Values ...........................................15 
     6       iSCSI Error Handling and Recovery .....................16 
     6.1     ITT ...................................................16 
     6.2     Format Errors .........................................16 
     6.3     Digest Errors .........................................16 
     7       Security Considerations ...............................18 
     8       IANA Considerations ...................................19 
     9       References and Bibliography ...........................20 
     9.1     Normative References ..................................20 
     9.2     Informative References ................................20 
     10      Editor's Address ......................................21 
     11      Acknowledgements ......................................22 
     12      Full Copyright Statement ..............................23 
     13      Intellectual Property Statement .......................24 
      





 
 
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1  Definitions and acronyms 

1.1  Definitions 

        I/O Buffer ¡ A buffer that is used in a SCSI Read or Write 
             operation so SCSI data may be sent from or received into 
             that buffer.  For a read or write data transfer to take 
             place for a task, an I/O Buffer is required on the 
             initiator and at least one required on the target. 

        SCSI-Presented Data Transfer Length (SPDTL): SPDTL is the 
             aggregate data length of the data that SCSI layer 
             logically "presents" to iSCSI layer for a Data-in or 
             Data-out transfer in the context of a SCSI task.  For a 
             bidirectional task, there are two SPDTL values ¡ one for 
             Data-in and one for Data-out.  Note that the notion of 
             "presenting" includes immediate data per the data 
             transfer model in [SAM2], and excludes overlapping data 
             transfers, if any, requested by the SCSI layer. 

        Third-party: A term used in this document to denote nexus 
             objects (I_T or I_T_L) and iSCSI sessions which reap the 
             side-effects of actions took place in the context of a 
             separate iSCSI session, while being third parties to the 
             action that caused the side-effects.  One example of a 
             Third-party session is an iSCSI session hosting an I_T_L 
             nexus to an LU that is reset with an LU Reset TMF via a 
             separate I_T nexus. 

         

1.2  Acronyms  

        Acronym        Definition 

        ------------------------------------------------------------- 

        EDTL              Expected Data Transfer Length 

        IANA           Internet Assigned Numbers Authority 

        IETF           Internet Engineering Task Force 

        I/O            Input - Output 

        IP             Internet Protocol 

        iSCSI          Internet SCSI 

        iSER           iSCSI Extensions for RDMA 



    
    
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     ITT            Initiator Task Tag 

     LO             Leading Only 

     LU             Logical Unit 

     LUN            Logical Unit Number 

     PDU            Protocol Data Unit 

     RDMA           Remote Direct Memory Access 

     R2T            Ready To Transfer 

     R2TSN          Ready To Transfer Sequence Number 

     RFC            Request For Comments 

     SAM            SCSI Architecture Model 

     SCSI           Small Computer Systems Interface 

     SN             Sequence Number 

     SNACK          Selective Negative Acknowledgment - also 

                    Sequence Number Acknowledgement for data 

     TCP            Transmission Control Protocol 

     TMF              Task Management Function 

     TTT            Target Transfer Tag 

     UA             Unit Attention 

      





 
 
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2  Introduction 

   Several iSCSI implementations had been built after [RFC3720] was 
   published and the iSCSI community is now richer by the resulting 
   implementation expertise.  The goal of this document is to 
   leverage this expertise both to offer clarifications to the 
   [RFC3720] semantics and to address defects in [RFC3720] as 
   appropriate.  This document intends to offer critical guidance 
   to implementers with regard to non-obvious iSCSI implementation 
   aspects so as to improve interoperability and accelerate iSCSI 
   adoption.  This document, however, does not purport to be an 
   all-encompassing iSCSI how-to guide for implementers, nor a 
   complete revision of [RFC3720].  This document instead is 
   intended as a companion document to [RFC3720] for the iSCSI 
   implementers. 

    

   iSCSI implementers are required to reference [RFC3722] and 
   [RFC3723] in addition to [RFC3720] for mandatory requirements.  
   In addition, [RFC3721] also contains useful information for 
   iSCSI implementers.  The text in this document, however, updates 
   and supersedes the text in all the noted RFCs whenever there is 
   such a question. 





    
    
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3  iSCSI semantics for SCSI tasks 

3.1  Residual handling 

Section 10.4.1 of [RFC3720] defines the notion of "residuals" 
and specifies how the residual information should be encoded 
into the SCSI Response PDU in Counts and Flags fields.  Section 
3.1.1 clarifies the intent of [RFC3720] and explains the general 
principles.  Section 3.1.2 describes the residual handling in 
the REPORT LUNS scenario. 

3.1.1  Overview 

SCSI-Presented Data Transfer Length (SPDTL) is the term this 
document uses (see section 1.1 for definition) to represent the 
aggregate data length that the target SCSI layer attempts to 
transfer using the local iSCSI layer for a task.  Expected Data 
Transfer Length (EDTL) is the iSCSI term that represents the 
length of data that iSCSI layer expects to transfer for a task.  
EDTL is specified in the SCSI Command PDU. 

 

When SPDTL = EDTL for a task, the target iSCSI layer completes 
the task with no residuals.  Whenever SPDTL differs from EDTL 
for a task, that task is said to have a residual. 

If SPDTL > EDTL for a task, iSCSI Overflow MUST be signaled in 
the SCSI Response PDU as specified in [RFC3720].  Residual Count 
MUST be set to the numerical value of (SPDTL ¡ EDTL). 

If SPDTL < EDTL for a task, iSCSI Underflow MUST be signaled in 
the SCSI Response PDU as specified in [RFC3720].  Residual Count 
MUST be set to the numerical value of (EDTL ¡ SPDTL). 

 

Note that the Overflow and Underflow scenarios are independent 
of Data-in and Data-out.  Either scenario is logically possible 
in either direction of data transfer. 

 

 

      





 
 
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3.1.2  SCSI REPORT LUNS and Residual Overflow 

The specification of the SCSI REPORT LUNS command requires that 
the SCSI target limit the amount of data transferred to a 
maximum size (ALLOCATION LENGTH) provided by the initiator in 
the REPORT LUNS CDB.  If the Expected Data Transfer Length 
(EDTL) in the iSCSI header of the SCSI Command PDU for a REPORT 
LUNS command is set to at least as large as that ALLOCATION 
LENGTH, the SCSI layer truncation prevents an iSCSI Residual 
Overflow from occurring.  A SCSI initiator can detect that such 
truncation has occurred via other information at the SCSI layer.  
The rest of the section elaborates this required behavior. 

 

iSCSI uses the (O) bit (bit 5) in the Flags field of the SCSI 
Response and the last SCSI Data-In PDUs to indicate that that an 
iSCSI target was unable to transfer all of the SCSI data for a 
command to the initiator because the amount of data to be 
transferred exceeded the EDTL in the corresponding SCSI Command 
PDU (see Section 10.4.1 of [RFC3720]). 

 

The SCSI REPORT LUNS command requests a target SCSI layer to 
return a logical unit inventory (LUN list) to the initiator SCSI 
layer (see section 6.21 of SPC-3 [SPC3]).  The size of this LUN 
list may not be known to the initiator SCSI layer when it issues 
the REPORT LUNS command; to avoid transfer of more LUN list data 
than the initiator is prepared for, the REPORT LUNS CDB contains 
an ALLOCATION LENGTH field to specify the maximum amount of data 
to be transferred to the initiator for this command.  If the 
initiator SCSI layer has under-estimated the number of logical 
units at the target, it is possible that the complete logical 
unit inventory does not fit in the specified ALLOCATION LENGTH.  
In this situation, section 4.3.3.6 in [SPC3] requires that the 
target SCSI layer "shall terminate transfers to the Data-In 
Buffer" when the number of bytes specified by the ALLOCATION 
LENGTH field have been transferred. 

 

Therefore, in response to a REPORT LUNS command, the SCSI layer 
at the target presents at most ALLOCATION LENGTH bytes of data 
(logical unit inventory) to iSCSI for transfer to the initiator.     
For a REPORT LUNS command, if the iSCSI EDTL is at least as 
large as the ALLOCATION LENGTH, the SCSI truncation ensures that 
the EDTL will accommodate all of the data to be transferred.  If 
all of the logical unit inventory data presented to the iSCSI 
layer ¡ i.e. the data remaining after any SCSI truncation - is 



 
 
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transferred to the initiator by the iSCSI layer, an iSCSI 
Residual Overflow has not occurred and the iSCSI (O) bit MUST 
NOT be set in the SCSI Response or final SCSI Data-Out PDU.  
This is not a new requirement but is already required by the 
combination of [RFC 3720] with the specification of the REPORT 
LUNS command in [SPC3].  If the iSCSI EDTL is larger than the 
ALLOCATION LENGTH however in this scenario, note that the iSCSI 
Underflow MUST be signaled in the SCSI Response PDU.  An iSCSI 
Underflow MUST also be signaled when the iSCSI EDTL is equal to 
ALLOCATION LENGTH but the logical unit inventory data presented 
to the iSCSI layer is smaller than ALLOCATION LENGTH. 

 

The LUN LIST LENGTH field in the logical unit inventory (first 
field in the inventory) is not affected by truncation of the 
inventory to fit in ALLOCATION LENGTH; this enables a SCSI 
initiator to determine that the received inventory is incomplete 
by noticing that the LUN LIST LENGTH in the inventory is larger 
than the ALLOCATION LENGTH that was sent in the REPORT LUNS CDB.  
A common initiator behavior in this situation is to re-issue the 
REPORT LUNS command with a larger ALLOCATION LENGTH. 

3.2  R2T Ordering 

Section 10.8 in [RFC3720] says the following: 

     The target may send several R2T PDUs. It, therefore, can have 
     a number of pending data transfers. The number of outstanding 
     R2T PDUs are limited by the value of the negotiated key 
     MaxOutstandingR2T. Within a connection, outstanding R2Ts MUST 
     be fulfilled by the initiator in the order in which they were 
     received. 

The quoted [RFC3720] text was unclear on the scope of 
applicability ¡ either per task, or across all tasks on a 
connection ¡ and may be interpreted as either.  This section is 
intended to clarify that the scope of applicability of the 
quoted text is a task.  No R2T ordering relationship ¡ either in 
generation at the target or in fulfilling at the initiator ¡ 
across tasks is implied.  I.e., outstanding R2Ts within a task 
MUST be fulfilled by the initiator in the order in which they 
were received on a connection. 

 

 





 
 
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4  Task Management 

4.1  Requests Affecting Multiple Tasks 

This section updates the original text in section 10.6.2 of 
[RFC3720].  The clarified semantics are a superset of the 
semantics of the original text in it the new text covers all 
TMFs that can impact multiple tasks. 

4.1.1  Scope of affected tasks 

       ABORT TASK SET: All outstanding tasks for the I_T_L nexus 
       identified by the LUN field in the ABORT TASK SET TMF 
       Request PDU. 

       CLEAR TASK SET: All outstanding tasks in the task set for 
       the LU identified by the LUN field in the CLEAR TASK SET 
       TMF Request PDU.  See [SPC3] for the definition of a "task 
       set". 

       LOGICAL UNIT RESET: All outstanding tasks from all 
       initiators for the LU identified by the LUN field in the 
       LOGICAL UNIT RESET Request PDU. 

       TARGET WARM RESET/TARGET COLD RESET: All outstanding tasks 
       from all initiators across all LUs that the TMF-issuing 
       session has access to on the SCSI target device hosting the 
       iSCSI session. 

Usage example: an "ABORT TASK SET TMF Request PDU" in the 
preceding text is an iSCSI TMF Request PDU with the "Function" 
field set to "ABORT TASK SET" as defined in [RFC3720].  Similar 
usage is employed for other scope descriptions. 

4.1.2  Updated semantics 

The execution of ABORT TASK SET, CLEAR TASK SET, LOGICAL UNIT 
RESET, TARGET WARM RESET, and TARGET COLD RESET TMF Requests 
consists of the following sequence of actions in the specified 
order on each of the entities.  

 
The initiator: 

     a) Issues ABORT TASK SET/CLEAR TASK SET/LOGICAL UNIT 
       RESET/TARGET WARM RESET/TARGET COLD RESET request. 

     b) Continues to respond to each TTT received for the affected 
       tasks.  




 
 
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  c) Receives any responses that the target may provide for some 
       tasks among the affected tasks (may process them as usual 
       because they are guaranteed to have chronologically 
       originated before the TMF response).  

     d) Receives the task management response concluding all the 
       tasks in the set of affected tasks.  
        
        

The Target MUST do the following: 

     a) Receives the ABORT TASK SET/CLEAR TASK SET/LOGICAL UNIT 
       RESET/TARGET WARM RESET/TARGET COLD RESET request. 

     b) Waits for all currently valid target transfer tags of the 
       affected tasks to be responded. 

     c) Based on the CmdSN ordering, waits (concurrent with the 
       wait in step (b)) for all commands of the affected tasks to 
       be received.  In the case of target-scoped requests (i.e. 
       TARGET WARM RESET and TARGET COLD RESET), all the commands 
       that are not received, as at the end of step (b), in the 
       command stream however can be considered to have been 
       received with no command waiting period - i.e. the entire 
       CmdSN space upto the CmdSN of the task management function 
       can be "plugged" (refer section 6.9 on how aborting a 
       specific task can implicitly plug the CmdSN of the task 
       being aborted) at the end of step (b).  

     d) Propagates the TMF request to and receives the response 
       from the target SCSI layer.  

     e) Takes note of last-sent StatSN on each of the connections 
       in the iSCSI session(s) (one or more) sharing the affected 
       tasks, and waits for acknowledgement of each StatSN (may 
       solicit for acknowledgement by way of a NOP-In).  If any 
       new task responses are meanwhile received from the SCSI 
       layer while waiting for StatSN acknowledgement(s), those 
       response PDUs ¡ the first SCSI Response PDU of which is 
       presumably carrying the UA notification on all Third-party 
       sessions - MUST be held and queued at the iSCSI layer.  If 
       some tasks originate from non-iSCSI I_T_L nexuses then the 
       means by which the target insures that all affected tasks 
       have returned their status to the initiator are defined by 
       the specific non-iSCSI transport protocol(s).  

     f) Sends the task set management response to the issuing 
       initiator.  All task response PDUs held back at the iSCSI 
       layer in step e are simultaneously eligible for being 



 
 
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       placed on the wire at this point. 
        

4.1.3  Rationale behind the new semantics 

There are fundamentally three basic objectives behind the 
semantics specified in section 4.1.2. 

     1.  Maintaining an ordered command flow I_T nexus abstraction 
            to the target SCSI layer even with multi-connection 
            sessions.   

             o  Target iSCSI processing of a TMF request must maintain 
                the single flow illusion - steps c & d of the target 
                behavior correspond to this objective. 

     2.  Maintaining a single ordered response flow I_T nexus 
            abstraction to the initiator SCSI layer even with multi-
            connection sessions when one response (i.e. TMF response) 
            could imply the status of other unfinished tasks from the 
            initiator's perspective.   

             o  Target must ensure that the initiator does not see 
                "old" task responses (that were placed on the wire 
                chronologically earlier than the TMF response) after 
                seeing the TMF response - step e of the target 
                behavior corresponds to this objective. 

             o  Whenever the result of a TMF action is visible across 
                multiple I_T_L nexuses, [SAM2] requires the SCSI 
                device server to trigger a UA on each of the other 
                I_T_L nexuses.  Once an initiator is notified of such 
                an UA, the application client on the receiving 
                initiator is required to clear its task state (clause 
                5.5 in [SAM2]) for the affected tasks.  It would thus 
                be inappropriate to deliver a SCSI Response for a task 
                after the task state is cleared on the initiator, i.e. 
                after the UA is notified.  The UA notification 
                contained in the first SCSI Response PDU on each 
                affected Third-party I_T_L nexus after the TMF action 
                thus MUST NOT pass the affected task responses on any 
                of the iSCSI sessions accessing the LU ¡ steps e & f 
                of the target behavior correspond to this objective. 
                 
                 

     3.  Draining all active TTTs corresponding to affected tasks 
            before the TMF is acted on.   





 
 
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       o  Targets are better off if the TTTs are 
          deterministically retired before the affected tasks 
          are terminated because that eliminates the possibility 
          of large-sized Data-out PDUs with stale TTTs arriving 
          after the tasks are terminated.  Step b of the target 
          behavior corresponds to this objective. 

 

The only other notable thing in step c of the target behavior is 
the "plugging" part - it is an optimization that says if all 
tasks on the I_T nexus will be aborted anyway (as with a target 
reset), there is no need to wait, the target can simply plug all 
missing CmdSN slots and move on with TMF processing.  The first 
objective (maintaining a single ordered command flow) is still 
met with this optimization because target SCSI layer only sees 
ordered commands. 





 
 
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5  Discovery semantics 

5.1  Error Recovery for Discovery Sessions 

The negotiation of the key ErrorRecoveryLevel is not required 
for Discovery sessions ¡ i.e. for sessions that negotiated 
"SessionType=Discovery" ¡ because the default value of 0 is 
necessary and sufficient for Discovery sessions.  It is however 
possible that some legacy iSCSI implementations might attempt to 
negotiate the ErrorRecoveryLevel key on Discovery sessions.  
When such a negotiation attempt is made by the remote side, a 
compliant iSCSI implementation MUST propose a value of 0 (zero) 
in response.  The operational ErrorRecoveryLevel for Discovery 
sessions thus MUST be 0.  This naturally follows from the 
functionality constraints [RFC3720] imposes on Discovery 
sessions. 

 

5.2  Reinstatement Semantics of Discovery Sessions 

Discovery sessions are intended to be relatively short-lived.  
Initiators are not expected to establish multiple Discovery 
sessions to the same iSCSI Network Portal (see [RFC3720]).  An 
initiator may use the same iSCSI Initiator Name and ISID when 
establishing different unique sessions with different targets 
and/or different portal groups.  This behavior is discussed in 
Section 9.1.1 of [RFC3720] and is, in fact, encouraged as 
conservative reuse of ISIDs.  ISID RULE in [RFC3720] states that 
there must not be more than one session with a matching 4-tuple: 
<InitiatorName, ISID, TargetName, TargetPortalGroupTag>.  While 
the spirit of the ISID RULE applies to Discovery sessions the 
same as it does for Normal sessions, note that some Discovery 
sessions differ from the Normal sessions in two important 
aspects: 

       Because [RFC3720] allows a Discovery session to be 
       established without specifying a TargetName key in the 
       Login Request PDU (let us call such a session an "Unnamed" 
       Discovery session), there is no Target Node context to 
       enforce the ISID RULE. 

       Portal Groups are defined only in the context of a Target 
       Node.  When the TargetName key is NULL-valued (i.e. not 
       specified), the TargetPortalGroupTag thus cannot be 
       ascertained to enforce the ISID RULE. 

 





 
 
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The following sections describe the two scenarios ¡ Named 
Discovery sessions and Unnamed Discovery sessions ¡ separately. 

 

5.2.1  Unnamed Discovery Sessions 

For Unnamed Discovery sessions, neither the TargetName nor the 
TargetPortalGroupTag is available to the targets in order to 
enforce the ISID RULE.  So the following rule applies. 

 

UNNAMED ISID RULE: Targets MUST enforce the uniqueness of the 
following 4-tuple for Unnamed Discovery sessions: 
<InitiatorName, ISID, NULL, TargetAddress>.  The following 
semantics are implied by this uniqueness requirement. 

 

Targets SHOULD allow concurrent establishment of one Discovery 
session with each of its Network Portals by the same initiator 
port with a given iSCSI Node Name and an ISID.  Each of the 
concurrent Discovery sessions, if established by the same 
initiator port to other Network Portals, MUST be treated as 
independent sessions ¡ i.e. one session MUST NOT reinstate the 
other.   

 

A new Unnamed Discovery session that has a matching 
<InitiatorName, ISID, NULL, TargetAddress> to an existing 
discovery session MUST reinstate the existing Unnamed Discovery 
session.  Note thus that only an Unnamed Discovery session may 
reinstate an Unnamed Discovery session. 

 

5.2.2  Named Discovery Sessions 

For a Named Discovery session, the TargetName key is specified 
by the initiator and thus the target can unambiguously ascertain 
the TargetPortalGroupTag as well.  Since all the four elements 
of the 4-tuple are known, the ISID RULE MUST be enforced by 
targets with no changes from [RFC3720] semantics.  A new session 
with a matching <InitiatorName, ISID, TargetName, 
TargetPortalGroupTag> thus will reinstate an existing session.  
Note in this case that any new iSCSI session (Discovery or 
Normal) with the matching 4-tuple may reinstate an existing 
Named Discovery iSCSI session. 



 
 
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5.3  TPGT Values 

SAM-2 and SAM-3 specifications incorrectly note in their 
informative text that TPGT value should be non-zero, although 
[RFC3720} allows the value of zero for TPGT.  This section is to 
clarify that zero value is expressly allowed as a legal value 
for TPGT.  A future revision of SAM will be corrected to address 
this discrepancy. 





 
 
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6  iSCSI Error Handling and Recovery 

6.1  ITT 

Section 10.19 in [RFC3720] mentions this in passing but noted 
here again for making it obvious since the semantics apply to 
the initiators in general.  An ITT value of 0xffffffff is 
reserved and MUST NOT be assigned for a task by the initiator.  
The only instance it may be seen on the wire is in a target-
initiated NOP-In PDU (and in the initiator response to that PDU 
if necessary). 

 

6.2  Format Errors 

Section 6.6 of [RFC3720] discusses format error handling.  This 
section elaborates on the "inconsistent" PDU field contents 
noted in [RFC3720].   

All initiator-detected PDU construction errors MUST be 
considered as format errors.  Some examples of such errors are: 

- NOP-In with a valid TTT but an invalid LUN 

- NOP-In with a valid ITT (i.e. a NOP-In response) and also a 
valid TTT 

- SCSI Response PDU with Status=CHECK CONDITION, but 
DataSegmentLength = 0 

 

6.3  Digest Errors 

Section 6.7 of [RFC3720] discusses digest error handling.  It 
states that "No further action is necessary for initiators if the discarded 
PDU is an unsolicited PDU (e.g., Async, Reject)" on detecting a 
payload digest error.  This is incorrect. 
 
 
An Asynchronous Message PDU or a Reject PDU carries the next 
StatSN value on an iSCSI connection, advancing the StatSN.  When 
an initiator discards one of these PDUs due to a payload digest 
error, the entire PDU including the header MUST be discarded.  
Consequently, the initiator MUST treat the exception like a loss 
of any other solicited response PDU ¡ i.e. it MUST use one of 
the following options noted in [RFC3720]: 




 
 
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     a)     Request PDU retransmission with a status SNACK. 

     b)     Logout the connection for recovery and continue the 
            tasks on a different connection instance. 

     c)     Logout to close the connection (abort all the commands 
            associated with the connection). 

 





 
 
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7  Security Considerations 

This document does not introduce any new security considerations 
other than those already noted in [RFC3720].   Consequently, all 
the iSCSI-related security text in [RFC3723] is also directly 
applicable to this document. 

      





 
 
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8  IANA Considerations 

This draft does not have any specific IANA considerations other 
than those already noted in [RFC3720]. 

      





 
 
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9  References and Bibliography 

9.1  Normative References 

     [RFC3720] Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, 
          M., and E. Zeidner, "Internet Small Computer Systems 
          Interface (iSCSI)", RFC 3720, April 2004. 

     [RFC3722] Bakke, M., "String Profile for Internet Small 
          Computer Systems Interface (iSCSI) Names", RFC 3722, April 
          2004. 

     [RFC3723] Aboba, B., Tseng, J., Walker, J., Rangan, V., and 
     F. Travostino, "Securing Block Storage Protocols over IP", 
     RFC 3723, April 2004.  

     [SPC3] T10/1416-D, SCSI Primary Commands-3. 

      

9.2  Informative References 

     [RFC3721] Bakke, M., Hafner, J., Hufferd, J., Voruganti, K., 
          and M. Krueger, "Internet Small Computer Systems Interface 
          (iSCSI) Naming and Discovery", RFC 3721, April 2004. 

     [iSER] Ko, M., Chadalapaka, M., Elzur, U., Shah, H., Thaler, 
          P., J. Hufferd, "iSCSI Extensions for RDMA", IETF 
          Internet Draft draft-ietf-ips-iser-04.txt (work in 
          progress),  June 2005. 

     [RFC2119] Bradner, S. "Key Words for use in RFCs to Indicate 
          Requirement Levels", BCP 14, RFC 2119, March 1997.  

     [SAM2] ANSI X3.366-2003, SCSI Architecture Model-2 (SAM-2). 

      





 
 
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10  Editor's Address 

     Mallikarjun Chadalapaka 
     Hewlett-Packard Company 
     8000 Foothills Blvd. 
     Roseville, CA 95747-5668, USA 
     Phone: +1-916-785-5621  
     E-mail: cbm@rose.hp.com  
           
      





 
 
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11  Acknowledgements 

     The IP Storage (ips) Working Group in the Transport Area of 
     IETF has been responsible for defining the iSCSI protocol 
     (apart from a host of other relevant IP Storage protocols).  
     The editor acknowledges the contributions of the entire 
     working group.   

     The following individuals directly contributed to identifying 
     [RFC3720] issues and/or suggesting resolutions to the issues 
     clarified in this document: David Black (REPORT LUNS/overflow 
     semantics), Gwendal Grignou (TMF scope), Mike Ko (digest 
     error handling for Asynchronous Message), Dmitry Fomichev 
     (reserved ITT), Bill Studenmund (residual handling, discovery 
     semantics), Ken Sandars (discovery semantics), Bob Russell 
     (discovery semantics), Julian Satran (discovery semantics), 
     Rob Elliott (T10 liaison, R2T ordering), Joseph Pittman(TMF 
     scope).  This document benefited from all these 
     contributions. 

      





 
 
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12  Full Copyright Statement 

     Copyright (C) The Internet Society (2005).  This document is 
     subject to the rights, licenses and restrictions contained in 
     BCP 78, and except as set forth therein, the authors retain 
     all their rights.  

     This document and the information contained herein are 
     provided on an "AS IS" basis and THE CONTRIBUTOR, THE 
     ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), 
     THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE 
     DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT 
     NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 
     HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES 
     OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 





 
 
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13  Intellectual Property Statement  

      The IETF takes no position regarding the validity or scope of    
      any Intellectual Property Rights or other rights that might 
      be   claimed to pertain to the implementation or use of the 
      technology described in this document or the extent to which 
      any license under such rights might or might not be 
      available; nor does it represent that it has made any 
      independent effort to identify any such rights.  Information 
      on the procedures with respect to rights in RFC documents can 
      be found in BCP 78 and BCP 79.  

      Copies of IPR disclosures made to the IETF Secretariat and 
      any    assurances of licenses to be made available, or the 
      result of an   attempt made to obtain a general license or 
      permission for the use of such proprietary rights by 
      implementers or users of this   specification can be obtained 
      from the IETF on-line IPR    repository at 
      http://www.ietf.org/ipr.  

      The IETF invites any interested party to bring to its 
      attention    any copyrights, patents or patent applications, 
      or other    proprietary rights that may cover technology that 
      may be required   to implement this standard.  Please address 
      the information to the IETF at ietf-ipr@ietf.org.  

  





 
 
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